Conditions and methods will continue to be refined toward attaining optimal development of in vitro chemical transformation of strain-2 guinea pig cells as a reproducible, quantitative and reliable assay for potential chemical carcinogens. Conditions promoting the neoplastic growth of the transformed cells in syngeneic guinea pigs will be investigated. These will include in addition to irradiation the employment of immunosuppressive agents such as anti-lymphocyte serum and corticosteroids to determine if the absence of tumor formation is the result of immunological rejection of the transformed cells by the syngeneic host. Cell surface antigens of the transformed cells will be further defined to aid in this study and as part of the investigation of the mechanism of carcinogenesis at the cellular level.